1. Field of the Invention
The present invention relates generally to lifting devices, and more particularly, to a wheelchair lift device to provide access to stages, platforms, risers and other elevated structures for individuals with disabilities.
2. Description of the Background Art
Under the Americans With Disabilities Act of 1990 (the “ADA”), the U.S. government required that public buildings be accessible to the disabled. For persons requiring a wheelchair for mobility, abrupt changes in floor elevation have to be modified to enable access by wheelchair. The ADA permits vertical lifting devices to be used instead of a ramp.
Lifting devices for the disabled are known in the prior art. For example, U.S. Pat. No. 5,105,915 (Gary) describes a lifting device having a car including fixed sides and short, one-piece ramps at each end. The car is raised and lowered by a pantograph jack including a hydraulic pump driven by an electric motor controlled by switches. The patent also describes several lifting devices of the prior art. Another wheelchair lifting device is disclosed in U.S. Pat. No. 6,182,798 to Brady, et al., and assigned to AGM Container Controls, Inc., the of the lift car, transparent walls, a loading ramp, a dock plate, a stage height sensor, and numerous safety features. In addition, U.S. Pat. No. 7,926,618, also assigned to the assignee of the present invention, discloses a lift device suitable for elevating wheel chair-bound individuals to stages or platforms.
Lift devices are known wherein the lifting forces are applied directly below the platform of the lift car that supports the occupant of the wheel chair. One advantage of lift devices is that the load borne by the platform of the lift car is directly supported by the lift mechanism. On the other hand, locating the lift mechanism directly below the lift platform presents a disadvantage. The lift mechanism always presents some thickness or depth, even when the lift is lowered, and by locating the lift mechanism directly below the lift platform, it is then virtually impossible to fully-lower the floor of the lift car flush with the floor. Accordingly, a loading ramp must then be provided to raise the wheel chair occupant from the ground up a few inches to the lift car floor when boarding the lift device. The loading ramp adds weight, cost, and complexity to the lift device.
One alternate technique which has been used in the past to avoid the need for a loading ramp is to house the lifting mechanism on the sides of the lift platform, rather than below the lift platform itself. However, applicant has discovered that, in certain circumstances, this alternate technique presents its own set of problems. When the lifting forces needed to elevate the lift car are applied to the sides of the lift car, the load borne by the floor of the lift car is transferred to the sides of the lift car. Under sufficient load, the floor of the lift car tends to bow downwardly. This bowing of the lift car floor exerts a torque upon the attached side walls of the lift car. As a result, the upper portions of the side walls of the lift car, which originally extended essentially vertically above the lower portions thereof when the lift car was lowered to the ground, now tilt inwardly toward each other. Angular deformation of the side walls of the lift car is problematic; for example, inward pressure exerted by the side walls upon the front entry gate (used when the lift is lowered) and the rear exit gate (used to exit the lift when raised to stage height) can “pinch” those gates, making them more difficult to open.
In view of the foregoing, it is an object of the present invention to provide a wheel chair lift device suitable for lifting wheelchair-bound users up to the height of stages, platforms, risers and the like in a safe and reliable manner, and comporting with all applicable ADA requirements.
Another object of the present invention is to provide such a lift device that is relatively inexpensive, easy to construct and use, and simple to maintain.
Still another object of the present invention is to provide such a lift device that is provided in a form that is easy to transport, and which can be collapsed to pass through narrow openings.
Yet another object of the present invention is to provide such a lift device wherein the lift car floor can be sufficiently lowered to the ground to avoid the need for an entry ramp, while avoiding deformation of the lift car side walls away from their usual vertical orientation.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.